1. Field of the Invention
The invention pertains first to a method for diagnosing a fuel injection device which has a piezoelectric actuator for actuating a valve element.
2. Description of the Prior Art
Particularly in internal combustion engines with direct fuel injection, fuel injection devices are used whose valve elements are actuated not electromagnetically but rather, at least indirectly, by the change in length of a piezoelectric actuator. The advantage of piezoelectric actuators is their very fast switching time and the very precise stroke adjustment that is possible. By using such fuel injection devices, the fuel can be introduced very precisely into the engine combustion chambers, which in turn leads to favorable emissions and low fuel consumption.
For the function of the engine, the correct function of the piezoelectric actuator therefore plays a central role, which in turn necessitates monitoring the correct function of the piezoelectric actuator. It is for instance known to determine the capacitance of the piezoelectric actuators used again and again during engine operation. If a major change in capacitance is found within a defined period of time, this is an indication of damage to the piezoelectric actuator, for instance. In that case, the fuel can no longer be introduced with the required precision into the combustion chamber of the engine by the corresponding fuel injection device.
If a fuel injection device is blocked in the opened position, this is also detected. In such a case, a compulsory shutdown of the engine may even be necessary. If a malfunction is detected, a fault entry is made in a fault memory. The stored fault data can be read out in a repair facility by a suitable diagnostic device. In this way, the mechanic learns the location and type of the fault that has occurred.
It is, therefore the object of the present invention to refine a method of the type defined at the outset such that the diagnosis of the fuel injection device can also be done “in the field”, that is, far away from a repair facility or a suitably equipped repair vehicle.